So-called "unit heaters" have seen extensive use in commercial and industrial settings. They are relatively easy to install and provide relatively high quantities of heat for the space that they occupy.
In the usual case, such heaters include a heat exchanger made up of several parallel tubes. The tubes are typically arranged vertically and their lower sections are of relatively large cross section to be aligned with a burner or the like and act as a combustor. The resulting flue gases resulting from combustion then travel upwardly within each of the tubes through a narrowed section. After the flue gas has exited the tubes, it is typically conducted away to a vent. Air flowing past either section of the tube on the exterior thereof is heated by the hot walls of the tube.
The present invention is directed to providing a new and improved tube construction for use in a heat exchanger of the sort mentioned and which is particularly suited for use in an improved unit heater to provide improved heat transfer efficiency.